CHEMICAL ENGINEERING posing a system, divided by maximum demand of the system. Thus assume a system consisting of three motors on which the maximum loads are respectively 100, 120 and 140 hp. The maximum load on the system will in general be less than the sum (360 1900 1800 1700 1600 1500 1400 £ 1300 •4- 1 IEOO ^o 2 '100 1000 900 800 TOO GOO 500, Avemt \L \el T 12 Ml. 8 10 12 2 Noon T(me A.M. FIG. 1.—Station load curves. 6 P.M. 10 12 Nt. hpO of, the individual maximums, because maximum loads are not apt to occur simultaneously. If the system maximum load is 180 hp. the DF = 2. It is desirable that it be low. The lowest possible value is 1. This will be realized when all units operate at steady loads. Time FIG. 2.—Load fluctuations. Demand factor is the ratio of maximum demand on a system to the total rated capacity of the connected load. It is related to the diversity factor much as load factor is related to capacity factor. In the illustration just given, if the three motors are each of 125 hp. rated capacity, the demand factor is 180 -f- 375 '= 0.48. This is a most important factor in considering a power installation. LF and DF depend on the load only: rated capacity and overload capacity on the equipment only: capacity factor, demand factor and reserve capacity on the load and equiDment iointlv.